Environment-friendly polypropylene insulating flame-retardant medium-voltage cable

Abstract

The invention relates to the technical field of cables, and particularly discloses an environment-friendly polypropylene insulating flame-retardant medium-voltage cable which comprises a cable core and a protective structure layer arranged outside the cable core. The cable core is provided with three power insulation wire cores and three tensile wire cores which are twisted together, and a flame-retardant filling rope which is filled in a twisting gap of the three power insulation wire cores and the three tensile wire cores, and each tensile wire core is arranged at a twisting outer side gap of two adjacent power insulation wire cores; each power insulation wire core is composed of a conductor, and a conductor shielding layer, a polypropylene insulation layer, an insulation shielding layer, a shielding isolation layer, a metal shielding composite layer and a conductor core fireproof layer which are sequentially arranged outside the conductor from inside to outside. According to the invention, the medium-voltage cable formed based on the polypropylene insulating material effectively gives consideration to good tensile property and bending resistance, so that the convenience, flexibility and stability of the medium-voltage cable when the medium-voltage cable is used in a working condition environment are improved.

Description

Technical Field

[0001] The invention relates to the technical field of cables, in particular to an environmentally friendly polypropylene insulated flame-retardant medium-voltage cable. Background Art

[0002] Medium voltage cables usually refer to power cables of 35kv and below. They are mainly used in petrochemical, transportation, wastewater treatment, food processing and other technical fields in real life and production. They are an important part of the power transmission and distribution network. Medium voltage cables have high technical requirements for electrical performance, heat resistance and flame retardancy.

[0003] Polypropylene material (i.e. PP material) is a milky white high-crystalline polymer that is light in volume and weight, non-toxic, odorless, tasteless, and easy to be environmentally friendly in the later stage. It not only has good electrical properties, but also has good heat resistance (it can increase the long-term operating temperature of the cable from 90°C to 105°C). It is very suitable for the insulation structure molding of medium-voltage cables. Compared with the cross-linked polyethylene insulation material (i.e. XLPE material) traditionally used in medium-voltage cables, it has the technical advantages of light weight, environmental protection, and heat resistance. Therefore, the development of medium-voltage cables made of polypropylene insulation materials has good market prospects. Based on this, the applicant previously disclosed a medium-voltage cable based on polypropylene insulation material, as detailed in the Chinese patent document entitled "An Environmentally Friendly Polypropylene Insulated Flame-Retardant and Fire-Resistant Medium-Voltage Cable", with a publication number of CN 118609888 A and a publication date of September 6, 2024.

[0004] However, the applicant discovered during research that polypropylene insulation materials have technical problems such as high hardness, high crystallinity and low flexibility during use, which results in poor performance of the molded medium voltage cable in terms of tensile strength and bending resistance, limiting the convenience, flexibility and stability of the use of medium voltage cables in working environments, which needs to be improved. Summary of the invention

[0005] The technical purpose of the present invention is to provide an environmentally friendly polypropylene insulated flame-retardant medium-voltage cable based on polypropylene insulation material with excellent tensile strength and bending resistance in view of the particularity of the above-mentioned medium-voltage cable and the shortcomings of the prior art.

[0006] The technical purpose of the present invention is achieved through the following technical scheme: an environmentally friendly polypropylene insulated flame-retardant medium-voltage cable, comprising a cable core and a protective structure layer arranged outside the cable core; The cable core comprises three power insulation cores and three tensile cores twisted together, and a flame retardant filling rope filled in the twisted gaps between the three power insulation cores and the three tensile cores, and each tensile core is arranged at the twisted outer gaps between two adjacent power insulation cores; The power insulated wire core is composed of a conductor and a conductor shielding layer, a polypropylene insulation layer, an insulation shielding layer, a shielding isolation layer, a metal shielding composite layer and a conductor core fireproof layer which are arranged in sequence from the inside to the outside of the conductor.

[0007] Furthermore, the conductor of the power insulated core is composed of a plurality of concentrically arranged circular conductors, a plurality of concentrically arranged fan-shaped conductors surrounding the outermost circular conductor, and a conductor wrapping layer arranged around each fan-shaped conductor; The concentrically arranged circular conductor and the sector-shaped conductor are a twisted structure; The conductor wrapping layer is an overlapping wrapping structure of a semi-conductive tape outside the sector-shaped conductor.

[0008] Furthermore, the power insulated wire core has a three-layer co-extruded structure of a conductor shielding layer, a polypropylene insulation layer and an insulation shielding layer.

[0009] Furthermore, the shielding isolation layer of the power insulating core is an overlapping wrapping structure of a semi-conductive tape outside the insulating shielding layer.

[0010] Furthermore, the metal shielding composite layer of the power insulating core is a composite structure of an inner copper wire sparse winding layer and an outer copper tape wrapping layer; Furthermore, a copper tape wrapping direction of the copper tape wrapping layer is opposite to a copper wire sparse winding direction of the copper wire sparse winding layer.

[0011] Furthermore, the conductor core fireproof layer of the power insulating core is an extruded structure of ceramic silicone rubber outside the metal shielding composite layer.

[0012] Furthermore, the tensile wire core is composed of a tensile core and a tensile core fireproof layer coated on the outside of the tensile core; The tensile core is a twisted structure of multiple aramid fiber strands; The fireproof layer of the tensile core is an extruded structure of ceramic silicone rubber outside the tensile core.

[0013] Furthermore, the protective structural layer outside the cable core is composed of a flame retardant wrapping layer, an oxygen barrier layer, an inner sheath layer, a metal armor layer and an outer sheath layer which are arranged in sequence from the inside to the outside of the cable core.

[0014] Furthermore, the flame retardant wrapping layer is an overlapping wrapping structure of ceramic silicone rubber mica composite tape on the outside of the cable core; The inner sheath layer is an extruded structure of a low-smoke, halogen-free, flame-retardant polyolefin material outside the oxygen-isolating layer; The outer sheath layer is an extruded structure of a low-smoke, halogen-free, flame-retardant polyolefin material outside the metal armor layer.

[0015] Furthermore, the metal armor layer is a double-layer sparsely wound armor structure in which a metal tape is outside the inner sheath layer; Alternatively, the metal armor layer is a densely wound armor structure of multiple strands of metal wires outside the inner sheath layer.

[0016] The beneficial technical effect of the present invention is: the above-mentioned technical measures are aimed at the particularity of the above-mentioned medium-voltage cable, and the insulation structure of the power insulating core is formed with a lightweight, environmentally friendly, and heat-resistant polypropylene insulation material. At the same time, in the cable core structure composed of the power insulating core, three tensile cores are arranged basically evenly distributed between the twisted gaps of the three power insulating cores. On the one hand, the three tensile cores jointly bear the axial tensile task of the formed cable, and on the other hand, the three circumferentially distributed tensile cores bear the traction force of the formed cable when it is bent and twisted according to the corresponding distribution positions. The tensile core of the aramid fiber strand structure is particularly good. This is because the aramid fiber strand has the technical characteristics of high tensile strength and low elongation at break. While meeting the axial tensile performance, it cooperates with the three tensile cores distributed at different circumferential positions to effectively bear the traction force when the cable is bent and twisted, thereby reliably compensating for the technical problems of poor tensile resistance and bending resistance of the power insulation core formed by the polypropylene insulation structure, so that the medium-voltage cable formed based on the polypropylene insulation material effectively takes into account good tensile resistance and bending resistance, so as to improve the convenience, flexibility and stability of this type of medium-voltage cable when used in working conditions.

[0017] In addition, in the above-mentioned technical measures, the tensile core is composed of a twisted structure of aramid fiber strands and an extruded structure of ceramic silicone rubber, which meets the above-mentioned tensile strength and bending resistance in the medium voltage cable and is suitable for the technical requirements of the medium voltage cable for heat resistance and flame retardancy, thereby forming a heat-resistant and flame retardant structure to reliably improve the heat resistance and flame retardancy of the formed medium voltage cable.

[0018] The conductor of the power insulated core is formed by concentrically arranged round conductors and fan-shaped conductors wrapped with semi-conductive tape, which can effectively reduce the skin effect of the medium-voltage cable during use and reliably improve the current-carrying capacity of the medium-voltage cable. At the same time, the wrapping structure of the semi-conductive tape can effectively prevent the three-layer co-extruded conductor shielding material and polypropylene insulation material from being embedded in the twisted structure of the conductor, so as to ensure that the aforementioned electrical properties of the conductor are not disturbed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A structural schematic diagram of the present invention.

[0020] Figure 2 for Figure 1 Schematic diagram of the power insulation core structure.

[0021] Figure 3 for Figure 2Schematic diagram of the conductor structure in .

[0022] Figure 4 for Figure 1 Schematic diagram of the tensile wire core structure.

[0023] The meaning of the codes in the figure are as follows: 1—power insulated core; 11—conductor; 111—round conductor; 112—sector-shaped conductor; 113—conductor winding layer; 12—conductor shielding layer; 13—polypropylene insulation layer; 14—insulation shielding layer; 15—shielding isolation layer; 16—metal shielding composite layer; 161—copper wire sparse winding layer; 162—copper tape winding layer; 17—conductor core fireproof layer; 2—tensile core; 21—tensile core; 22—tensile core fireproof layer; 3—flame retardant filling rope; 4—flame retardant winding layer; 5—oxygen insulation layer; 6—inner sheath layer; 7—metal armor layer; 8—outer sheath layer. DETAILED DESCRIPTION

[0024] The present invention relates to the field of cable technology, and more specifically to an environmentally friendly polypropylene insulated flame-retardant medium voltage cable. The main technical solution of the present invention is described in detail below in conjunction with a number of embodiments. Figure 1 , Figure 2 , Figure 3 and Figure 4 The technical solution of the present invention is explained clearly and in detail; although other embodiments are not separately drawn with drawings, their main structures can still refer to the drawings of embodiment 1.

[0025] It should be noted that the drawings of the present invention are schematic, and unnecessary details have been simplified to clarify the technical purpose of the present invention, so as to avoid blurring the technical solution of the present invention that contributes to the prior art. In addition, the expressions "approximately", "substantially" and the like regarding quantity or matching relationship in the following text mean that reasonable assembly errors and processing errors in the industry are allowed to exist, and do not literally express absolute quantities or matching relationships.

[0026] Example 1 See also Figure 1 As shown, the medium voltage cable of the present invention comprises a cable core and a flame retardant wrapping layer 4, an oxygen barrier layer 5, an inner sheath layer 6, a metal armor layer 7 and an outer sheath layer 8 which are sequentially arranged outside the cable core from the inside to the outside.

[0027] The cable core has three power insulation cores 1 and three tensile cores 2 twisted together, and a flame retardant filling rope 3 filled in the twisted gap between the three power insulation cores 1 and the three tensile cores 2, and the twisted pitch ratio is about 30 times. Each tensile core 2 is arranged at the outer gap of the twisted two adjacent power insulation cores 1, so that in the use of the formed medium voltage cable, the three tensile cores 2 jointly bear the axial tensile task - that is, to form anti-axial tensile performance, and the three circumferentially distributed tensile cores 2 bear the traction force of the formed cable when bending and twisting according to the corresponding distribution position - that is, to form anti-bending performance.

[0028] See also Figure 2 and Figure 3 As shown, the above-mentioned power insulating core 1 is composed of a conductor 11 and a conductor shielding layer 12, a polypropylene insulation layer 13, an insulation shielding layer 14, a shielding isolation layer 15, a metal shielding composite layer 16 and a conductor core fireproof layer 17 arranged in sequence from the inside to the outside outside the conductor 11 to form a power insulating core based on polypropylene insulation material. Compared with traditional cross-linked polyethylene insulation materials, a light, environmentally friendly and heat-resistant power insulating core is obtained.

[0029] Among them, Figure 3 As shown, the conductor 11 of the power insulated core 1 is composed of a plurality of concentrically arranged round conductors 111 (copper), a plurality of concentrically arranged fan-shaped conductors 112 (copper) surrounding the outermost round conductor 111, and a conductor wrapping layer 113 arranged around each fan-shaped conductor 112. The concentrically arranged round conductors 111 and the fan-shaped conductors 112 are twisted structures. The conductor wrapping layer 113 is a single-layer overlapping wrapping structure of a semi-conductive tape outside the fan-shaped conductor 112, with an overlapping wrapping rate of about 30%. The conductor wrapping layer 113 tightens the twisted round conductors 111 and fan-shaped conductors 112. The conductor 11 of this structure can not only effectively reduce the skin effect of the formed medium-voltage cable, reliably increase the current carrying capacity of the medium-voltage cable, but also effectively prevent the tip discharge phenomenon caused by the conductor shielding material and the insulating material embedded in the twisted gap of the metal conductor, and has excellent electrical performance.

[0030] See also Figure 4 As shown, the tensile core 2 is composed of a tensile core 21 and a tensile core fireproof layer 22 coated on the outside of the tensile core 21. The tensile core 21 is a twisted structure of multiple aramid fiber strands with high tensile strength and low elongation at break. The tensile core fireproof layer 22 is an extruded structure of heat-resistant and flame-retardant ceramic silicone rubber on the outside of the tensile core 21. The tensile core 2 of this structure not only meets the technical requirements of tensile performance in the formed medium-voltage cable, but is also heat-resistant and flame-retardant, and can effectively adapt to the technical performance requirements of medium-voltage cables for heat resistance and flame retardancy.

[0031] In the molding structure of the above-mentioned power insulated core 1, the conductor shielding layer 12, the polypropylene insulation layer 13 and the insulation shielding layer 14 are semi-conductive and adopt a three-layer co-extrusion structure alternating with polypropylene insulation material, which not only meets the insulation performance requirements, but also can effectively balance the electric field of the conductor 11.

[0032] In the molding structure of the above-mentioned power insulating core 1, the shielding isolation layer 15 is a single-layer overlapping winding structure of a semi-conductive tape outside the insulating shielding layer 14, and the overlapping winding rate is about 30%. While balancing the electric field of the conductor 11, it reliably separates the metal shielding composite layer and the insulating shielding layer 14, thereby preventing the metal shielding composite layer 16 from damaging the insulating shielding layer 14 and the internal polypropylene insulating layer 13.

[0033] In the molding structure of the above-mentioned power insulating core 1, the metal shielding composite layer 16 is a composite structure of an inner copper wire sparse winding layer 161 and an outer copper tape wrapping layer 162. The copper tape wrapping layer 162 is a single-layer overlapping wrapping structure of copper tape, and the overlapping wrapping rate is about 30%. Moreover, the copper tape wrapping direction of the copper tape wrapping layer 162 is opposite to the copper wire sparse winding direction of the copper wire sparse winding layer 161, so that the molding structure of the metal shielding composite layer 16 is compact, stable, and not easy to loosen, ensuring that its electromagnetic shielding performance is maintained for a long time.

[0034] In the molding structure of the above-mentioned power insulating core 1, the conductor core fireproof layer 17 is an extruded structure of ceramic silicone rubber outside the metal shielding composite layer 16, so that the molded power insulating core 1 obtains heat resistance and flame retardant properties, which effectively adapts to the technical performance requirements of medium voltage cables for heat resistance and flame retardancy.

[0035] In the molding structure of the above-mentioned medium voltage cable, the flame retardant wrapping layer 4 is a single-layer overlapping wrapping structure of ceramicized silicone rubber mica composite tape on the outside of the cable core, and the overlapping wrapping rate is about 30%. On the one hand, it tightens and rounds the molding structure of the cable core, and on the other hand, it enables the cable core to obtain heat-resistant and flame-retardant properties, which effectively adapts to the technical performance requirements of medium voltage cables for heat resistance and flame retardancy.

[0036] In the molded structure of the medium voltage cable, the oxygen-isolating layer 5 is an extruded structure of fluoroplastic outside the flame-retardant wrapping layer 4 .

[0037] In the molded structure of the medium voltage cable, the inner sheath layer 6 is an extruded structure of a low-smoke, halogen-free, flame-retardant polyolefin material outside the oxygen-isolating layer 5 .

[0038] In the molded structure of the above-mentioned medium voltage cable, the metal armor layer 7 is a double-layer sparsely wound armor structure of metal tapes outside the inner sheath layer 6, which can obtain a certain degree of softness while obtaining impact-resistant structural strength.

[0039] In the molded structure of the medium voltage cable, the outer sheath layer 8 is an extruded structure of a low-smoke, halogen-free, flame-retardant polyolefin material outside the metal armor layer 7 .

[0040] The above medium voltage cable is prepared according to the following process steps: Step 1. Prepare power insulation wire cores: obtain three power insulation wire cores; Preparation of tensile wire cores; obtaining three tensile wire cores; Step 2. On a 3150 cable drum machine, three power insulation cores and three tensile cores are twisted together with the flame-retardant filling ropes of the stranded structure according to the above-mentioned phase distribution method according to the designed pitch ratio to obtain a cable core of a twisted structure; Step 3. Overlapping and wrapping the ceramic silicone rubber mica composite tape on the outside of the cable core according to the designed overlap rate to obtain a flame retardant wrapping layer; Step 4. Extruding fluoroplastic on the outside of the flame retardant wrapping layer according to the designed thickness to obtain an oxygen barrier layer; Step 5. Extruding an inner sheath layer of low-smoke halogen-free flame-retardant polyolefin material outside the oxygen barrier layer according to the designed extrusion thickness; Step 6. On the outside of the inner sheath layer, double-layer metal armor layers of the metal tape structure are sequentially wound according to the designed winding pitch; Step 7. Extrude an outer sheath layer of low-smoke halogen-free flame-retardant polyolefin material on the outside of the metal armor layer according to the designed extrusion thickness; Get flame retardant medium voltage cables.

[0041] In the above step 1, the preparation of the power insulating core includes the following process steps: Step ①. Using a double-head continuous annealing wire drawing machine, through 7 passes of the die, the φ8mm copper rod is stretched and shaped into a round wire of the required specifications to obtain multiple round conductors; A double-head continuous annealing wire drawing machine is used to stretch and shape the φ8mm copper rod into a fan-shaped wire of the required specifications through 7 passes of the die to obtain multiple fan-shaped conductors; Step ②. Arrange multiple conductors of circular wire structure into concentric circles; Distributing a plurality of fan-shaped conductors of the fan-shaped wire structure on the periphery of the circular conductors distributed in the concentric circle structure; The wires are twisted into strands by a frame-type stranding machine, and a semi-conductive tape is wrapped around the outer surface of the stranded metal conductor to obtain a conductor wrapping layer; Step ③. The semi-conductive conductor shielding material, polypropylene insulating material and semi-conductive insulating shielding material are sequentially extruded in a three-layer co-extrusion manner on the outside of the conductor in step ② to obtain a three-layer co-extrusion structure of the conductor shielding layer, polypropylene insulating layer and insulating shielding layer; At the same time, the wire core exiting the die head is cooled in sections and in stages by nitrogen pressurization (nitrogen pressure is 1.0MPa) + water cooling. The nitrogen pressurization cooling area is divided into 8 sections, the water vapor transition area is divided into 2 sections, and the water cooling area is divided into 12 sections. The temperature distribution of each section of the nitrogen boost cooling area is shown in Table 1 below:

[0042] Step ④. Wrap the semi-conductive tape around the outside of the insulating shielding layer according to the designed overlap rate to obtain a shielding isolation layer; Step ⑤. Wind the copper wire sparsely according to the designed pitch, sparsely wind it outside the shielding isolation layer, and obtain a sparsely wound copper wire layer; Step ⑥. Wrap the copper tape around the outside of the copper wire sparse winding layer according to the designed overlap rate and winding direction to obtain a copper tape wrapped layer; Step ⑦. On a 120 extruder, the ceramic silicone rubber is extruded on the outside of the copper tape wrapping layer according to the designed thickness to obtain a conductor core fireproof layer; A heat-resistant and flame-retardant power insulation wire core with a polypropylene insulation structure is obtained.

[0043] In the above step 1, the preparation of the tensile wire core includes the following process steps: Step ①. Twisting the aramid yarn to obtain multiple aramid strands; Step ②. Twisting multiple aramid strands together in a concentric circle distribution structure; Step ③. Extruding ceramic silicone rubber onto the outside of the aramid strand twisted structure of step ② to obtain a tensile wire core.

[0044] The power insulation core obtained by the segmented cooling method of nitrogen pressurization + water cooling mentioned above has been shown by comparative tests (the difference in the comparative tests is only in the change of cooling method, and the others are the same) to effectively prevent the internal stress accumulation and plastic stratification of the power insulation core due to rapid cooling, and at the same time effectively reduce the adverse effects of gravity factors on the eccentricity of cable insulation.

[0045] Comparative Example 1 directly uses water cooling, and the distribution of each section of the cooling area is shown in Table 2 below:

[0046] Comparative Example 2 adopts the unsegmented nitrogen boosting (nitrogen pressure 1.0 MPa) + water cooling method; the temperature distribution of each section of the nitrogen boosting cooling area is shown in Table 3 below:

[0047] Comparative Example 3 uses nitrogen boosting (nitrogen pressure 1.0 MPa) + water cooling under different temperature conditions; the temperature distribution of each section of the nitrogen boosting cooling area is shown in Table 4 below:

[0048] The cooling method and temperature conditions of the present invention, and the power insulation core structure and performance parameters obtained by the three comparative examples described above are shown in Table 5 below:

[0049] It can be clearly seen from the contents shown in Table 5 that the present invention adopts a segmented nitrogen pressurized cooling + water cooling method under specific temperature conditions. On the one hand, the specific nitrogen pressurization can increase the pressure on the surface of the power insulating core, so that the insulation shielding layer, the polypropylene insulation layer, and the conductor shielding layer are more tightly bonded to prevent the occurrence of stratification; on the other hand, nitrogen is an inert gas, which plays a good protective role on the power insulating core.

[0050] Example 2 The medium voltage cable of the present invention comprises a cable core and a flame retardant wrapping layer, an oxygen isolation layer, an inner sheath layer, a metal armor layer and an outer sheath layer which are sequentially arranged outside the cable core from the inside to the outside.

[0051] The cable core has three power insulation cores and three tensile cores twisted together, and a flame retardant filling rope filled in the gap between the three power insulation cores and the three tensile cores, and the twisted pitch ratio is about 25 times. Each tensile core is arranged at the outer gap of the twisted two adjacent power insulation cores. In this way, in the use of the formed medium-voltage cable, the three tensile cores jointly bear the axial tensile task - that is, to form anti-axial tensile performance, and the three circumferentially distributed tensile cores bear the traction force of the formed cable when bending and twisting according to the corresponding distribution position - that is, to form anti-bending performance.

[0052] The above-mentioned power insulating core is composed of a conductor and a conductor shielding layer, a polypropylene insulation layer, an insulating shielding layer, a shielding isolation layer, a metal shielding composite layer and a conductor core fireproof layer arranged in sequence from the inside to the outside of the conductor to form a power insulating core based on polypropylene insulation material. Compared with traditional cross-linked polyethylene insulation materials, a light, environmentally friendly and heat-resistant power insulating core is obtained.

[0053] Among them, the conductor of the power insulated core is composed of multiple concentrically arranged round conductors (copper), multiple sector-shaped conductors (copper) concentrically arranged around the outermost circular conductor, and a conductor sheath arranged around each sector-shaped conductor. The concentrically arranged round conductors and sector-shaped conductors are twisted structures. The conductor sheath is a single-layer overlapping wrapping structure of a semi-conductive tape on the outside of the sector-shaped conductor, with an overlapping wrapping rate of about 45%. The conductor sheath tightens the twisted round conductors and sector-shaped conductors. The conductor of this structure can not only effectively reduce the skin effect of the formed medium-voltage cable and reliably increase the current carrying capacity of the medium-voltage cable, but also effectively prevent the tip discharge phenomenon caused by the conductor shielding material and insulating material embedded in the twisted gap of the metal conductor, and has excellent electrical performance.

[0054] The tensile core is composed of a tensile core and a tensile core fireproof layer coated on the outside of the tensile core. The tensile core is a twisted structure of multiple aramid fiber strands with high tensile strength and low elongation at break. The tensile core fireproof layer is an extruded structure of heat-resistant and flame-retardant ceramic silicone rubber on the outside of the tensile core. The tensile core of this structure not only meets the technical requirements of tensile performance in the formed medium-voltage cable, but also has heat resistance and flame retardancy, and can effectively meet the technical performance requirements of medium-voltage cables for heat resistance and flame retardancy.

[0055] In the molding structure of the above-mentioned power insulated wire core, the conductor shielding layer, the polypropylene insulation layer and the insulation shielding layer are semi-conductive and adopt a three-layer co-extrusion structure alternately with the polypropylene insulation material, which not only meets the insulation performance requirements, but also can effectively balance the electric field of the conductor.

[0056] In the molding structure of the above-mentioned power insulating core, the shielding isolation layer is a single-layer overlapping winding structure of a semi-conductive tape outside the insulating shielding layer, and the overlapping winding rate is about 45%. While balancing the electric field of the conductor, it reliably separates the metal shielding composite layer and the insulating shielding layer, thereby preventing the metal shielding composite layer from damaging the insulating shielding layer and the internal polypropylene insulation layer.

[0057] In the molding structure of the above-mentioned power insulating core, the metal shielding composite layer is a composite structure of an inner copper wire sparse winding layer and an outer copper tape winding layer, and the copper tape winding layer is a single-layer overlapping winding structure of copper tape, and the overlapping winding rate is about 45%. Moreover, the copper tape winding direction of the copper tape winding layer is opposite to the copper wire sparse winding direction of the copper wire sparse winding layer, so that the molding structure of the metal shielding composite layer is compact, stable, and not easy to loosen, thereby ensuring that its electromagnetic shielding performance is maintained for a long time.

[0058] In the above-mentioned molding structure of the power insulating core, the conductor core fireproof layer is an extruded structure of ceramic silicone rubber on the outside of the metal shielding composite layer, so that the molded power insulating core has heat resistance and flame retardant properties, which effectively adapts to the technical performance requirements of medium voltage cables for heat resistance and flame retardancy.

[0059] In the molding structure of the above-mentioned medium voltage cable, the flame retardant wrapping layer is a single-layer overlapping wrapping structure of ceramicized silicone rubber mica composite tape on the outside of the cable core, and the overlapping wrapping rate is about 45%. On the one hand, it tightens and rounds the molding structure of the cable core, and on the other hand, it enables the cable core to obtain heat-resistant and flame-retardant properties, which effectively adapts to the technical performance requirements of medium voltage cables for heat resistance and flame retardancy.

[0060] In the molded structure of the medium voltage cable, the oxygen-isolating layer is an extruded structure of fluoroplastic outside the flame-retardant wrapping layer.

[0061] In the molded structure of the above-mentioned medium voltage cable, the inner sheath layer is an extruded structure of a low-smoke, halogen-free, flame-retardant polyolefin material outside the oxygen-isolating layer.

[0062] In the molded structure of the above-mentioned medium voltage cable, the metal armor layer is a densely wound armor structure of multiple metal wires outside the inner sheath layer, which can obtain a certain degree of softness while obtaining impact-resistant structural strength.

[0063] In the molded structure of the above-mentioned medium voltage cable, the outer sheath layer is an extruded structure of low-smoke halogen-free flame-retardant polyolefin material outside the metal armor layer.

[0064] Example 3 The medium voltage cable of the present invention comprises a cable core and a flame retardant wrapping layer, an oxygen isolation layer, an inner sheath layer, a metal armor layer and an outer sheath layer which are sequentially arranged outside the cable core from the inside to the outside.

[0065] The cable core has three power insulation cores and three tensile cores twisted together, and a flame retardant filling rope filled in the gap between the three power insulation cores and the three tensile cores, and the twisted pitch ratio is about 35 times. Each tensile core is arranged at the outer gap of the twisted two adjacent power insulation cores. In this way, in the use of the formed medium-voltage cable, the three tensile cores jointly bear the axial tensile task - that is, to form anti-axial tensile performance, and the three circumferentially distributed tensile cores bear the traction force of the formed cable when bending and twisting according to the corresponding distribution position - that is, to form anti-bending performance.

[0066] The above-mentioned power insulating core is composed of a conductor and a conductor shielding layer, a polypropylene insulation layer, an insulating shielding layer, a shielding isolation layer, a metal shielding composite layer and a conductor core fireproof layer arranged in sequence from the inside to the outside of the conductor to form a power insulating core based on polypropylene insulation material. Compared with traditional cross-linked polyethylene insulation materials, a light, environmentally friendly and heat-resistant power insulating core is obtained.

[0067] Among them, the conductor of the power insulated core is composed of multiple concentrically arranged round conductors (copper), multiple sector-shaped conductors (copper) concentrically arranged around the outermost circular conductor, and a conductor sheath arranged around each sector-shaped conductor. The concentrically arranged round conductors and sector-shaped conductors are twisted structures. The conductor sheath is a single-layer overlapping wrapping structure of a semi-conductive tape on the outside of the sector-shaped conductor, with an overlapping wrapping rate of about 50%. The conductor sheath tightens the twisted round conductors and sector-shaped conductors. The conductor of this structure can not only effectively reduce the skin effect of the formed medium-voltage cable and reliably increase the current carrying capacity of the medium-voltage cable, but also effectively prevent the tip discharge phenomenon caused by the conductor shielding material and insulating material embedded in the twisted gap of the metal conductor, and has excellent electrical performance.

[0068] The tensile core is composed of a tensile core and a tensile core fireproof layer coated on the outside of the tensile core. The tensile core is a twisted structure of multiple aramid fiber strands with high tensile strength and low elongation at break. The tensile core fireproof layer is an extruded structure of heat-resistant and flame-retardant ceramic silicone rubber on the outside of the tensile core. The tensile core of this structure not only meets the technical requirements of tensile performance in the formed medium-voltage cable, but also has heat resistance and flame retardancy, and can effectively meet the technical performance requirements of medium-voltage cables for heat resistance and flame retardancy.

[0069] In the molding structure of the above-mentioned power insulated wire core, the conductor shielding layer, the polypropylene insulation layer and the insulation shielding layer are semi-conductive and adopt a three-layer co-extrusion structure alternately with the polypropylene insulation material, which not only meets the insulation performance requirements, but also can effectively balance the electric field of the conductor.

[0070] In the molding structure of the above-mentioned power insulating core, the shielding isolation layer is a single-layer overlapping winding structure of a semi-conductive tape outside the insulating shielding layer, and the overlapping winding rate is about 50%. While balancing the electric field of the conductor, it reliably separates the metal shielding composite layer and the insulating shielding layer, thereby preventing the metal shielding composite layer from damaging the insulating shielding layer and the internal polypropylene insulating layer.

[0071] In the molding structure of the above-mentioned power insulating core, the metal shielding composite layer is a composite structure of an inner copper wire sparse winding layer and an outer copper tape winding layer, and the copper tape winding layer is a single-layer overlapping winding structure of copper tape, and the overlapping winding rate is about 50%. Moreover, the copper tape winding direction of the copper tape winding layer is opposite to the copper wire sparse winding direction of the copper wire sparse winding layer, so that the molding structure of the metal shielding composite layer is compact, stable, and not easy to loosen, thereby ensuring that its electromagnetic shielding performance is maintained for a long time.

[0072] In the above-mentioned molding structure of the power insulating core, the conductor core fireproof layer is an extruded structure of ceramic silicone rubber on the outside of the metal shielding composite layer, so that the molded power insulating core has heat resistance and flame retardant properties, which effectively adapts to the technical performance requirements of medium voltage cables for heat resistance and flame retardancy.

[0073] In the molding structure of the above-mentioned medium voltage cable, the flame retardant wrapping layer is a single-layer overlapping wrapping structure of ceramicized silicone rubber mica composite tape on the outside of the cable core, and the overlapping wrapping rate is about 50%. On the one hand, it tightens and rounds the molding structure of the cable core, and on the other hand, it enables the cable core to obtain heat-resistant and flame-retardant properties, which effectively adapts to the technical performance requirements of medium voltage cables for heat resistance and flame retardancy.

[0074] In the molded structure of the medium voltage cable, the oxygen-isolating layer is an extruded structure of fluoroplastic outside the flame-retardant wrapping layer.

[0075] In the molded structure of the above-mentioned medium voltage cable, the inner sheath layer is an extruded structure of a low-smoke, halogen-free, flame-retardant polyolefin material outside the oxygen-isolating layer.

[0076] In the molded structure of the above-mentioned medium voltage cable, the metal armor layer is a double-layer sparsely wound armor structure with metal tapes outside the inner sheath layer, which can obtain a certain degree of softness while obtaining impact-resistant structural strength.

[0077] In the molded structure of the above-mentioned medium voltage cable, the outer sheath layer is an extruded structure of low-smoke halogen-free flame-retardant polyolefin material outside the metal armor layer.

[0078] The above embodiments are only used to illustrate the present invention, but not to limit it.

[0079] Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the above embodiments or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not deviate the essence of the corresponding technical solutions from the spirit and scope of the present invention.

Claims

1. An environmentally friendly polypropylene insulated flame-retardant medium-voltage cable, comprising a cable core and a protective structure layer arranged outside the cable core; Features: The cable core comprises three power insulation cores (1) and three tensile cores (2) twisted together, and a flame retardant filling rope (3) filled in the twisted gaps between the three power insulation cores (1) and the three tensile cores (2), and each tensile core (2) is arranged at the outer gaps between the twisted ends of two adjacent power insulation cores (1); The power insulated wire core (1) is composed of a conductor (11) and a conductor shielding layer (12), a polypropylene insulation layer (13), an insulation shielding layer (14), a shielding isolation layer (15), a metal shielding composite layer (16) and a conductor core fireproof layer (17) arranged in sequence from the inside to the outside outside the conductor (11).

2. The environmentally friendly polypropylene insulated flame-retardant medium voltage cable according to claim 1, characterized in that: The conductor (11) of the power insulated core (1) is composed of a plurality of concentrically arranged circular conductors (111), a plurality of concentrically arranged sector-shaped conductors (112) surrounding the outermost circular conductor (111), and a conductor sheath (113) arranged surrounding each sector-shaped conductor (112); The concentrically arranged circular conductor (111) and the fan-shaped conductor (112) are of a twisted structure; The conductor wrapping layer (113) is an overlapping wrapping structure of a semi-conductive tape outside the fan-shaped conductor (112).

3. The environmentally friendly polypropylene insulated flame-retardant medium voltage cable according to claim 1, characterized in that: The power insulating wire core (1) has a three-layer co-extruded structure of a conductor shielding layer (12), a polypropylene insulating layer (13) and an insulating shielding layer (14).

4. The environmentally friendly polypropylene insulated flame-retardant medium voltage cable according to claim 1, characterized in that: The shielding isolation layer (15) of the power insulating core (1) is an overlapping wrapping structure of a semi-conductive tape outside the insulating shielding layer (14).

5. The environmentally friendly polypropylene insulated flame-retardant medium voltage cable according to claim 1, characterized in that: The metal shielding composite layer (16) of the power insulating core (1) is a composite structure of an inner copper wire sparse winding layer (161) and an outer copper tape wrapping layer (162); Furthermore, the copper tape wrapping direction of the copper tape wrapping layer (162) is opposite to the copper wire sparse winding direction of the copper wire sparse winding layer (161).

6. The environmentally friendly polypropylene insulated flame-retardant medium voltage cable according to claim 1, characterized in that: The conductor core fireproof layer (17) of the power insulating wire core (1) is an extruded structure of ceramic silicone rubber outside the metal shielding composite layer (16).

7. The environmentally friendly polypropylene insulated flame-retardant medium voltage cable according to claim 1, characterized in that: The tensile wire core (2) is composed of a tensile core (21) and a tensile core fireproof layer (22) coated on the outside of the tensile core (21); The tensile core (21) is a twisted structure of multiple aramid fiber strands; The tensile core fireproof layer (22) is an extruded structure of ceramic silicone rubber on the outside of the tensile core (21).

8. The environmentally friendly polypropylene insulated flame-retardant medium voltage cable according to claim 1, characterized in that: The protective structural layer outside the cable core is composed of a flame retardant wrapping layer (4), an oxygen barrier layer (5), an inner sheath layer (6), a metal armor layer (7), and an outer sheath layer (8) arranged in sequence from the inside to the outside of the cable core.

9. The environmentally friendly polypropylene insulated flame-retardant medium voltage cable according to claim 8, characterized in that: The flame retardant wrapping layer (4) is an overlapping wrapping structure of ceramicized silicone rubber mica composite tape on the outside of the cable core; The inner sheath layer (6) is an extruded structure of a low-smoke, halogen-free, flame-retardant polyolefin material outside the oxygen-isolating layer (5); The outer sheath layer (8) is an extruded structure of a low-smoke, halogen-free, flame-retardant polyolefin material outside the metal armor layer (7).

10. The environmentally friendly polypropylene insulated flame-retardant medium voltage cable according to claim 8, characterized in that: The metal armor layer (7) is a double-layer sparsely wound armor structure in which a metal belt is outside the inner sheath layer (6); Alternatively, the metal armor layer (7) is a densely wound armor structure of multiple strands of metal wires outside the inner sheath layer (6).

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